Recent data collected from 73 native grassland soils throughout the North American Great Plains show a strong inverse relationship between latitude and stable C isotopes of organic matter and a strong direct relationship between stable C isotopes of organic matter and mean July temperature. Consequently, stable C isotopes from buried paleosol organic matter should be a reliable proxy for soil biomass production from C4 plants and temperatures in the past. A literature compilation of 202 stable C isotope values from radiocarbon-dated buried paleosols in fluvial and eolian environments was analyzed for the last 12,000 years from Texas (29.5°N) to North Dakota (46.5°N) to establish latitudinal trends. A second-order polynomial regression equation was used to transfer stable C isotope values to mean July temperatures. C4 soil biomass production from 12-11 ka indicates that temperatures were 2 to 3°C cooler than present at all latitudes. During the Younger Dryas, C4 production points to a temperature increase of approximately 1°C at all latitudes. From 11-7 ka C4 production and temperatures stabilized at Younger Dryas levels. However, from 7-5 ka C4 production levels transfer to a temperature increase of nearly 2°C, approximating the modern stable carbon isotope-temperature curve in both magnitude and shape at all latitudes. Slight variations in C4 production and temperature occurred during the last 5 ka, but were maintained near-modern levels. Throughout the North American Great Plains, fossil pollen data suggests that relative to present temperatures were -3 to -6°C at 12 ka, –2 to 0°C at 9 ka, and 0 to +2°C at 6 ka. All temperature estimates using the C4 transfer function in this study fall within the range of pollen estimates. Importantly, a cooling episode associated with the Young Dryas was not recognized, and maximum C4 production occurred 2000 years after attainment of maximum summer solar insolation at 9 ka. In contrast to current thinking, flourishing of C4 plants during the middle Holocene took place during a rapid rise in atmospheric CO2 from 220 to 280 ppmV. A new C4 soil biomass transfer function for temperature provides a much needed climate proxy that can be applied more pervasively throughout the Great Plains than fossil pollen.